A 32-year-old man with HIV (CD4 count 80 cells/microL) presents with progressive dyspnea, dry cough, and fever over 3 weeks. Chest X-ray shows bilateral diffuse interstitial infiltrates. Lavage fluid shows foamy eosinophilic exudate with cup-shaped organisms on methenamine silver stain. What is the causative organism?
- A Mycobacterium tuberculosis
- B Cytomegalovirus
- C Pneumocystis jirovecii ✓
- D Aspergillus fumigatus
Correct answer: C. Pneumocystis jirovecii
Explanation
Pneumocystis jirovecii pneumonia (PCP) occurs in immunocompromised patients with CD4 below 200 cells/microL. The classic presentation is bilateral diffuse interstitial infiltrates with foamy eosinophilic alveolar exudate containing cup-shaped cysts on methenamine silver stain. CMV shows owl eye inclusions. TB would show granulomas. Aspergillus shows septate hyphae with acute angle branching.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.